We inherited a pond with goldfish 10 years ago. All seems very happy and they continue to breed with just the occasional deceased body. A few days ago I noticed Big Boy lying on his (her?) side on the bottom in the sun, the plants and water lilies not having yet emerged. Did not try to hide from my shadow, so I thought he was a gonner. I lifted him out but noticed that colour, condition and eyes were very bright. Only just gone? I laid him in the net on the ground and as I turned him over, I thought his ventral fins moved slightly, or was it just me turning him over. So I put him back in the pond and he did move but still appeared sluggish. Since then he has continued to improve and is swimming around seemingly happily. He appears to be the biggest in the pond. Was this some sort of behaviour I should have ignored? I don't know how old he is but he is about 7" long and very bright golden colour.

I think a change in behavior could be a sign of a problem. Keep a close eye on him. Is his dorsal fin staying up? Is he still socializing with the other fish? Any spots or lesions on him, or frayed fins?

If over the next few days it seems like his health is declining, maybe you can quarantine him so you can watch him better and treat for disease if necessary.